Heat dissipating devices, such as heatsinks, are known in the art of solid state electronics technology. Such devices are used to cool solid state components and printed circuit boards that have heat generated from the condensely packaged solid state components. Many circuit boards and individual solid state components must be cooled since excessive elevated temperatures could cause a change in the electrical performance or degrade the materials of the boards and components, leading to possible failure of the boards and components themselves. Consequently, in order for many solid state components to function properly, the heat must be removed to maintain proper operating temperatures for the components. Many attempts have been made to construct a low-cost and high-efficiency heatsink that can cool an individual circuit component, component package, or circuit board in a limited amount of space. However, so far such attempts have been unsuccessful in satisfying all of these objectives.
Many conventional heatsinks, such as pin-fin heatsinks and channeled-fin heatsinks, require the costly step of machining or channeling out a hollow area in the electrical device or platform where the heatsinks are inserted or mounted. Many of these heatsinks, such as channeled-fins, are removably inserted into channels requiring an additional structure, such as expansible conduits. These additional structures increase manufacturing costs. Moreover, because most of these heatsinks require hollow spaces or insulating inserts between the heat-generating component and the cooling device to operate, the heat flow from the heat-generating component is impaired and therefore the cooling device cannot effectively dissipate heat.
It is also known in the art to cool electronic devices by providing a conductive link of material, such as conductive pistons or spring elements, between the device and cap of a cold plate. The conductive links must be capable of forming a good interface contact over as large an area as possible in order to maintain a low thermal resistance. With cooling pistons, interfaces are difficult to form because the devices may be tilted, resulting in unsatisfactory point or line contact. To solve this problem, a conformal means is often used at the piston end to interface with the device. Unfortunately, the conformal means adds thermal resistance and increases costs.
Another example of conductive links is provided by U.S. Pat. No. 5,014,117 to Horvath, et al., where a set of fins and corresponding clips are used to convey heat from integrated circuit chips to a cold plate. In this patent, a miniature heat-conducting plate is placed over each chip. Each miniature plate has a plurality of short, rigid vertical fins at its top surface. The cold plate has a corresponding plurality of clips, each of which has two spring-loaded sides which abut against either side of a respective rigid vertical fin of the miniature plate. The sides of each clip are angled toward one another such that each compresses against a corresponding side of the rigid fin of the miniature plate. The clips conduct heat from the rigid fins to the cold plate through their points of compressive contact. No cooling fluid is passed through the clips or the rigid fins. The compressive contact enables the miniature plate to confirm to the tilt of the chip, and enables the miniature plate and clip to move with respect to one another in the vertical direction. Such vertical movement occurs when the chip heats up and cools down. Spring bias means are included to continually force the miniature plate against the chip. While this approach is better than the piston approach at accommodating chip tilts, it requires more components, is more expensive, and it is somewhat less efficient at conducting heat.
Many other prior art heatsinks use thick and relatively expensive metal fins which are cooled directly by a cooling fluid (e.g., cooling air, or cooling liquid). Each metal fin can readily conduct heat along its length because of the metal's low thermal resistance, but is not able to efficiently couple heat to the cooling fluid unless the cooling fluid is forced through the fins at a high velocity. The low coupling efficiency is due to the formation of a static layer of cooling fluid around the fin and the fact that the thermal resistance of the static layer is much larger than the thermal resistance of the metal fin. In order to reach the flow of the cooling fluid, the heat from the fin must be conducted through the static layer by diffusion. Increasing the velocity of the cooling fluid decreases the thickness of the static layer, thereby increasing the diffusion rate of heat through the static layer. Unfortunately, the increased velocity requires a corresponding high pressure drop in the fluid flow through the heatsink, which increases the cost of operating the heatsink. As an alternative to increasing the velocity of cooling fluid, the surface area of the fins could be increased by increasing the dimensions of the fins. However, this approach increases the cost and size of the packaged components. For these reasons, the thick-fin heatsinks have not been able to efficiently dissipate large amounts of heat from small volumes of space without the need for high velocities and large pressure drops in the cooling fluid.
A representative of devices that suffer from the above-detailed disadvantages, in that the heatsinks utilize thick rigid fins or rods, as compared to the present invention for cooling electronic components, is provided below. U.S. Pat. No. 4,897,712 to Prokopp is directed toward a heatsink having a base body, on which the structural elements and a cooling element are arranged next to each other. The cooling element includes a bundle of ribs consisting of a plurality of rigid sheets arranged parallel and at a distance to one another. The sheets may be held together via a soldered bridge and are connected with one another in a material connecting manner to form a bundle of ribs, which are then connected to the base body in a material connecting manner, where the thickness of the ribs vary with the number of sheets used. In addition, intermediate sheets are interposed between the cooling sheets for determining the spacing between the cooling sheets.
U.S. Pat. No. 5,299,090, to Brady, et al. relates to a heatsink which has a bundle of rods mounted on the outer surface of an integrated circuit package. The rods are secured at one end with a retainer and are flared out at the other end into a starburst configuration. The rods may be selected from solid cylinders and tubes. However, the bundling of the rods renders a significant portion of the rods' collective surface area useless for cooling purposes. Accordingly, the heat sink of Brady et al. has a lower heat dissipation capability because of the limited surface area provided by the flared configuration of the rods. Accordingly, higher air flow rates and corresponding greater pressure drops are needed for cooling, which diminishes the attempt to achieve high heat dissipation rates low operating costs.
U.S. Pat. No. 5,406,451 to Korinsky is directed toward a heatsink which is attached to a heat-producing component and which is disposed within the housing of a personal computer in a region of substantially linear airflow caused by an outward flowing fan. For a base, the heatsink has a flat metal sheet which is attached to the component at one of its edges, rather than at one of its surfaces. The heatsink also has several long fingers extending from one or more of the remaining edges of the sheet. These fingers are arranged in rows parallel to the direction of linear airflow, each row being set at a different angle so that the tips of one row of fingers are spaced apart from the tips of the next row of fingers. The arrangement of the fingers create turbulence in the airflow, which acts to reduce the thickness of static layer of cooling fluid which surrounds the fingers. The turbulence thus enables the air flow to receive more heat from the fingers, and enables heat from the heat-producing component to be extracted more rapidly. In the disclosure in Korinsky the fingers are thick and rigid, operate with only a linear air flow, and occupy a relatively small portion of the space spanned by the heat sink. Due to this last feature, the velocity and pressure drop must be relatively high to create an adequate amount of turbulence.
In many of the foregoing references, the use of rather thick and rigid fins are disclosed for air cooling, which do not accomplish the goal of having an inexpensive efficient heatsink capable of dissipating a large amount of heat energy in a limited space. Although thick and rigid metal fins are extremely conductive, they are not efficient at coupling their heat to the flow of the cooling fluid due to the static layer of cooling fluid that forms around them. Turbulence improves this coupling, but thus far has not been as effectively employed as has been done in the present invention.